On March 21st, the Eyjafjallajokull volcano in southern Iceland commenced a basaltic fissure eruption. Increasing seismic activity had been detected in the area for several weeks prior to the eruption, which caused some concern that a summit eruption would lead to volcanic flooding, as the summit of the volcano is covered by a large glacier. However, the eruption actually occurred on the flank of the volcano, and was not under the glacier.
The eruption began as a relatively small "curtain of fire" of lava fountains. The eruptive activity has now built a small cinder cone. It is possible to actually view a live Webcam view of the eruption here: Reykavik Hekla Volcano Webcam
Here is a description of the eruption, from the Nordic Volcanological Center and Icelandic Meteorological Office:
The eruption broke out with fire fountains and Hawaiian eruptive style on about 500 m long NE-SW oriented eruptive fissure at N63º 38.1′, W19º 26.4′ on the northeast shoulder of the volcano at an elevation of about 1000 m. It was observed from air from 4-7 A.M. on March 21. Lava flows short distance from the eruptive site, and minor eruption plume at elevation less than 1 km was deflected by wind to the west. Volcanic explosive index (VEI) is 1 or less. Tephra fall is minor or insignificant. The eruption occurs just outside the ice cap of Eyjafjallajökull, and no ice melting is occurring at present.
One of the data products in Giovanni that can be used to detect volcanic activity is the Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) data product. The release of ash and volcanic gas from an eruption will be observed as in increase in the value of AOD.
MODIS also has high-resolution thermal bands that allow detection of fires and the heat of lava flows. A MODIS thermal image (with an inset map showing the location of the eruption) is below.
A plot of the AOD values from March 19-22 is shown below. The location of the elevated AOD values on this plot on the coast of Iceland (which looks like an upside-down rainbow-striped mushroom) is the roughly the same as the location of the eruption.
This is a relatively small eruption, and thus it is not releasing a large quantity of volcanic gases. So this apparent detection, despite the gaps in coverage (the white areas in the plot), demonstrates the capabilities of MODIS.
To check the association of the elevated AOD values with the timing of the eruption, a time-series of AOD for the affected area (between 63-64°N and 19-20°W) was created. The plot, shown below, shows that the increase in AOD occurred on the same day as the start of the eruption.
While the "circumstantial evidence" indicates that the likely cause of the elevated MODIS AOD was the volcanic eruption, there is one other phenomenon that can increase AOD over Iceland -- dust storms. While dust storms may be more commonly thought of as occurring in desert climates, the large amount of glacial flour created by the glaciers in Iceland can also be mobilized by strong winds. The MODIS image below from January 2002 shows one such dust storm, also in southern Iceland and off the coast, as an area of grayish-brown swirling dust. It is possible that the other areas of elevated AOD that are visible in the second image could be due to dust from island.
So it is not totally certain that the elevated AOD observed by MODIS is due to the eruption; additional observations and more imagery can help to confirm the linkage between the volcano and its effects on the atmosphere.